K.C. Crowder

Washington University in St. Louis, Saint Louis, MO, United States

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Publications (9)22.57 Total impact

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    ABSTRACT: Liquid perfluorocarbon nanoparticles serve as sensitive and specific targeted contrast and drug delivery vehicles by binding to specific cell surface markers. We hypothesized that application of acoustic energy at diagnostic power levels could promote nanoparticle-associated drug delivery by stimulating increased interaction between the nanoparticle's lipid layer and the targeted cell's plasma membrane. Ultrasound (mechanical index = 1.9) applied with a conventional ultrasound imaging system to nanoparticles targeted to alpha(v)beta3-integrins on C32 melanoma cancer cells in vitro produced no untoward effects. Within 5 min, lipid delivery from nanoparticles into cell cytoplasm was dramatically augmented. We also demonstrate the operation of a potential physical mechanism for this effect, the acoustic radiation force on the nanoparticles, which may contribute to the enhanced lipid delivery. Accordingly, we propose that local delivery of lipophilic substances (e.g., drugs) from targeted nanoparticles directly into cell cytoplasm can be augmented rapidly and safely with conventional ultrasound imaging devices through nondestructive mechanisms.
    Ultrasound in Medicine & Biology 01/2006; 31(12):1693-700. · 2.46 Impact Factor
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    ABSTRACT: Not Available
    Ultrasonics Symposium, 2005 IEEE; 10/2005
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    ABSTRACT: Previous work has demonstrated the ability of liquid perfluorocarbon (PFC) nanoparticles to deliver therapeutic agents to cells selectively by binding to specific cellular epitopes, and confirmed the ability to simultaneously image these targeted nanoparticles with ultrasound. In this study, enhanced delivery of targeted PFC nanoparticles to cells expressing the integrin avb3 using clinical levels of ultrasound energy were studied. Nanoparticles complexed with ligands targeted to avb3 were incubated with cells (C32 melanoma) that expressed avb3 in culture. Control nanoparticles were produced that carried no ligand targeted to avb3. A custom specimen holder permitted simultaneous microscopic visualization of cell interactions during exposure to calibrated levels of ultrasound energy. After nanoparticle binding to cells and application of ultrasound, a roughly 2-fold increase in PFC content of the cells was observed. For control (nonbinding) nanoparticles, ultrasound exposure also increased PFC deposition, but the overall level was substantially less. Videodensitometric data show that nanoparticles were not destroyed by ultrasound exposure. Moreover, the alignment of nanoparticles relative to incident acoustic field demonstrate conclusively that acoustic radiation forces influence the nanoparticles and implicate these forces as participates in the enhanced delivery.
    The Journal of the Acoustical Society of America 01/2005; 117:2472-2472. · 1.65 Impact Factor
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    ABSTRACT: Liquid perfluorocarbon nanoparticle contrast agents can be used to target specific tissue types through incorporation of appropriate ligands into the nanoparticles' outer lipid monolayer. In this study we sought to characterize the specificity of targeting of perfluorooctyl bromide (PFOB) nanoparticles to tissue factor, a transmembrane glycoprotein expressed by smooth muscle cells as part of inflammatory response after vessel injury (e.g., angioplasty). Porcine smooth muscle cells constitutively expressing tissue factor on the cell surface were cultured on microporous membranes and targeted with PFOB nanoparticles by avidin-biotin binding techniques. Treatment groups included: 1) "targeted" cell samples exposed sequentially to biotinylated tissue factor antibody/avidin/biotinlyated nanoparticles, 2) "non-targeted" smooth muscle cells exposed to avidin/biotinlyated nanoparticles; 3) "control" smooth muscle cells left untreated. Ultrasonic imaging and quantification of surface reflectivity for each cell group was accomplished by scanning a 25MHz transducer in a grid over the membrane inserts and analyzing the reflected RF signal from the cell-covered surfaces. Total PFOB content for each sample (directly related to nanoparticle concentration) was determined independently by gas chromatography. Targeted cells exhibited significantly enhanced surface reflectivity (-22.6±2.0 dB referenced to steel reflector, p<0.002) relative to either non-targeted (-29.6±1.1 dB) or control groups (-29.3±1.4 dB). Gas chromatography data indicated that bound PFOB was present in targeted cells at levels nearly six times greater than for nontargeted cells. Additionally, bound PFOB levels for the targeted samples Correlated directly with the magnitude of surface reflectivity (r=0.99; p<0.03). In conclusion, PFOB nanoparticles targeted to smooth muscle cell tissue factor specifically bind to such cells at levels nearly six times greater than to nontargeted cells. The targeted cells exhibit substantially enhanced acoustic reflectivity, thereby confirming the utility of quantitative ultrasonic molecular imaging with the use of a nongaseous nanoparticle contrast agent.
    Ultrasonics Symposium, 2004 IEEE; 09/2004
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    ABSTRACT: Before molecular imaging with MRI can be applied clinically, certain problems, such as the potential sparseness of molecular epitopes on targeted cell surfaces, and the relative weakness of conventional targeted MR contrast agents, must be overcome. Accordingly, the conditions for diagnostic conspicuity that apply to any paramagnetic MRI contrast agent with known intrinsic relaxivity were examined in this study. A highly potent paramagnetic liquid perfluorocarbon nanoparticle contrast agent ( approximately 250 nm diameter, >90,000 Gd3+/particle) was imaged at 1.5 T and used to successfully predict a range of sparse concentrations in experimental phantoms with the use of standard MR signal models. Additionally, we cultured and targeted the smooth muscle cell (SMC) monolayers that express "tissue factor," a glycoprotein of crucial significance to hemostasis and response to vascular injury, by conjugating an anti-tissue factor antibody fragment to the nanoparticles to effect specific binding. Quantification of the signal from cell monolayers imaged at 1.5 T demonstrated, as predicted via modeling, that only picomolar concentrations of paramagnetic perfluorocarbon nanoparticles were required for the detection and quantification of tissue factor at clinical field strengths. Thus, for targeted paramagnetic agents carrying high payloads of gadolinium, it is possible to quantify molecular epitopes present in picomolar concentrations in single cells with routine MRI.
    Magnetic Resonance in Medicine 04/2004; 51(3):480-6. · 3.27 Impact Factor
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    ABSTRACT: Our laboratory previously has demonstrated the ability of liquid perfluoro-carbon (PFC) nanoparticles to serve as site-targeted contrast and therapeutic agents by specifically binding molecular markers. In this study, we sought to enhance the delivery of targeted PFC nanoparticles to cells expressing the integrin α<sub>v</sub>β<sub>3</sub> using clinical levels of ultrasound energy. Using an Acuson Sequoia imager, we demonstrate that ultrasound applied at 2MHz and 1.9 mechanical index (MI) for a five minute duration enhances the cellular interaction of targeted perfluorocarbon nanoparticles by melanoma cancer cells in vitro without any untoward effect from the ultrasound energy itself upon either the cells or the perfluorocarbon nanoparticles. Employing a custom designed specimen chamber, we have visualized a fundamental physical mechanism for this effect, that of acoustic radiation force (primary and secondary) on the particles, that may contribute to enhanced delivery. Accordingly, our study shows that enhancement of cellular interaction with targeted nanoparticles is feasible by noncavitational mechanisms. Ultrasonically-enhanced delivery of tracers or drugs to a wide variety of pathologic tissues may be useful for augmenting drug delivery after targeting, while limiting untoward effects on other tissues.
    Ultrasonics, 2003 IEEE Symposium on; 11/2003
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    ABSTRACT: Advances in molecular biology and cellular biochemistry are providing new opportunities for diagnostic medical imaging. Molecular imaging provides an opportunity to "see" the earliest biochemical signatures of disease in vivo analogous to microscopic detection of epitopes with immunohistochemistry techniques. Previously the province of nuclear medicine, today numerous, highly active research programs can be found for all clinically relevant imaging modalities. In many instances, these emerging site-directed imaging agents also incorporate therapeutic agents for drug delivery, allowing noninvasive confirmation and quantification of the targeted therapeutic dose. We have developed a novel multi-modal site-targeted contrast agent for sensitive and specific imaging of molecular epitopes and local therapy, which illustrates the key features of these emerging platform technologies. Targeted nanoparticles are applicable to ultrasound, nuclear, CT, and magnetic resonance imaging and have been used to detect a variety of epitopes expressed on angiogenic vessels, thrombus, and within vascular walls. Moreover, this particular targeted agent can deposit a therapeutic payload through a unique mechanism termed "contact-facilitated delivery". The combined benefits of molecular imaging and therapeutic systems are merging and will potentially alter many current clinical paradigms in the next decade.
    Ultrasonics, 2003 IEEE Symposium on; 11/2003
  • Journal of The American College of Cardiology - J AMER COLL CARDIOL. 01/2003; 41(6):59-59.
  • Circulation 01/2003; 108(17):644-644. · 15.20 Impact Factor